Students wait for the arrival of Labour MP Lucy Powell at Manchester Met business school in Manchester Thomson Reuters By Andy Bruce

LONDON (Reuters) - The campaign to keep Britain in the European Union extended its lead over the "Out" campaign in an opinion poll published on Saturday, while two major bookmakers offered the shortest odds to date on a vote to remain.

The poll from market research company Opinium for the Observer newspaper marked the sixth poll out of seven published in the last week to show the Remain campaign in the lead.

Forty-four percent of Britons wanted to remain in the EU, up from 42 percent in an Opinium/Observer poll at the end of last month, while the proportion wanting to leave edged down a point to 40 percent.

Earlier, William Hill and Ladbrokes cut their odds on Britain remaining in the European Union to 1/6, meaning gamblers would get only one pound ($1.45) in profit for every 6 pounds wagered if Britons vote to stay in the EU.

As polls have given sharply different pictures of public opinion, many investors are watching betting odds closely. Odds have consistently indicated a high probability of an "In" result in the June 23 referendum.

"There does seem to have been some move towards staying in the EU, particularly given that ours is an online methodology which typically shows a closer race than polls conducted on the phone," Adam Drummond of Opinium Research said.

Telephone polls have tended to show a larger lead for the "Remain" campaign, with online surveys instead suggesting the referendum result will be too close to call. Opinium surveyed 2,008 adults between May 17 and 19.

"The change comes mainly from Conservative voters who have moved from narrowly backing Brexit at the end of April to a large lead for remain," Drummond added.

The two bookmakers said the vast majority of cash staked on the referendum backed a "Remain" result - 90 percent of it in the case of Ladbrokes. Still, William Hill said most individual gamblers had betted on Britain leaving the EU.

"The Brexit rally of a few weeks ago seems a distant memory. It's significant that so many people are prepared to back remain despite the short odds," Ladbrokes spokesman Alex Donohue said in a statement.

William Hill's odds now reflect an 85 percent chance of a "Remain" vote, up from 83 percent on Friday. Ladbrokes, which removes the margin it takes on bets from its calculations, pointed to a 79 percent chance - up from 66 percent a month ago.

Earlier on Saturday, finance leaders of the Group of Seven industrial powers united over the weekend in wishing that Britain stays in the EU, but acknowledged they could do little more than hope.